After items are purchased and ordered through an electronic marketplace, the order may be sent to a fulfillment center, where the items of the order may be retrieved from storage and assembled together for shipment. In various scenarios, items may be ordered in virtually any combination, which means people must be tasked with retrieving the items so that they can be combined for shipment. Additionally, because a given fulfillment center may have thousands of items, items that are to be combined in an order may be stored at disparate locations throughout a fulfillment center.
In some scenarios, in order to efficiently allow people to retrieve items, systems may provide for mobile shelving units (“MSUs”), which may include mobile robots that may be utilized along with shelving units containing bins of items which may be ordered. In such scenarios, an MSU may, under computer control, be assigned to a person tasked with retrieving items for shipment (herein referred to as an “operator”). The MSU may travel to the operator, who may receive an indication of one or more items that are intended to be retrieved from the MSU. The operator may then retrieve the item(s) from the mobile shelving unit and set the item(s) aside for later shipment.
In order to most efficiently utilize the MSUs, in some scenarios each MSU may include shelves at different height levels, such that each unit has bins of items at different levels. While this may allow for greater utilization of each MSU, in many scenarios, an operator may find that they cannot always comfortably reach the bin from which they are to retrieve items, either because the items are too high or too low. In such situations, sometimes the operators must resort to using ladders to reach the needed items. Such special circumstances can result in an inefficient usage of time and slower overall fulfillment, which is undesirable.